As an example, in Fig. REF , we plot the SGWB from primordial BBHs produced in the context of the SM thermal history, with the primordial power spectrum of \(\tilde{n}_s=0.97\)  and no running. We compare it with the Power-Law-Sensitivity (PLS) curves [1]} of future GW experiments obtained by requiring a signal-to-noise ratio (SNR) of the measured SGWB of \({\rm SNR}=10\)  (see Section  for a detailed description of how the PLS is computed). As we can see in the figure, future GW experiments can cover the wide range of frequencies from \(10^{-9}\)  to \(10^3\)  Hz. At low frequencies, we consider SKA, which will work as a PTA observatory, and GAIA [2]} and THEIA, which will be used as GW observatories by monitoring the apparent position of stars (see e.g. Refs. [3]}, [4]}, [5]}, [6]}). At intermediate frequencies, we show the PLS curves of two space-based observatories, i.e. LISA and DECIGO/BBO. Finally, at the higher frequencies, we show the PLS for combinations of advanced LIGO, Virgo, and KAGRA and of the Einstein Telescope and the Cosmic Explorer (ET+CE), as considered in Ref. [7]}. We note, however, that several other GW experiments are planned that have sensitivity ranges overlapping with those considered here. In addition to the PLS curves, we also plot the constraints on the amplitude of the SGWB obtained by assuming that it is responsible for the stochastic common process signal detected by NANOGrav [8]} and the Parkes PTA [9]} and the upper bound from the LVK O3 run in the range of \([20,\,77]\)  Hz [10]}.
